WATER-BEETLES, the numerous species of beetles which inhabit water. A common mode of life does not indicate blood relation ship, and the various aquatic beetles belong to a number of quite distinct families. Besides those which are aquatic throughout their lives quite a large number of beetles live in or near the water only during the larval period. The strictly and permanently aquatic beetles belong chiefly to three families. The diving beetles (Dyisseide) are predaceous throughout life and represent in the water the Cardbsder, to which they are somewhat closely related, on land. The legs in these Insects are adapted for swim ming, the two hinder pairs being flattened and fringed with hairs. The body is oval and flat tened. The mandibles are short and strong and the thorax is broad. The front legs are short and the antenna long and filifortn. In the genus Dytircies the tarsi of the males are wide, flat and provided with sucking discs, while those of the females are unmodified. The females are of two forms, the one having the wing-covers smooth, the other grooved.. The head is short and received into the thorax. D. fasterentris is the common water-beetle of our ponds. These insects carry a supply of air for breathing beneath the rlylra or wing-covers. At evening they fly in the air. They are emi nently carnivorous in habits and feed on other insects. The larvae are active creatures and are also aquatic; their noteworthy rapacity has gained for them the name of water-tigers, which they well merit, for they will not hesitate to seize in their sharp sickle-like jaws any insect-. larva, small fish or tadpole that comes within reach, and after draining its juices discard the dead body. The tail is terminated by a pair of respiratory tubes which are raised above the surface of the water to effect respiration. Be sides this large species the family includes numerous small ones having sisnikr tidbits. The other two families have ciub-shape instead of filiform antenna.
The , or whirligig beetles, have the antenna short, the front Pegs tong, clawed, and in the males provided with a spongy disc, the second and third pairs of legs very short, broad and paddle-shaped, and the elynti do net cover the tip of the oval body. They derive their familiar name from their peculiar habit of de scribing circle on the surface of the pools they inhabit. When alarmed these insects Wive to the bottom and anchor themselves for a time by means of the strong front legs, carrying with them a small bubble of air an the tip of the abdomen. Owing to their smooth, polished and
oily surface they are unaffected by the water. The facets of the compound eyes are divided into two groups on each side, one adapted for vision in the water, and looking downward, the other for looking upward in the air—an im portant adaptation to the peculiar mode of life of these insects on the surface. When handled, the whirligigs emit from the joints a peculiar strong-smelling milky fluid. Although, like the Dytisees larvae. the young of the whirligigs are predaceous, their appearance is totally differ ent; they are of slender form and, instead of • single pair of caudal respiratory tubes or gills, they bear 10 pairs of fnnged lateral gills on the sides of as many abdominal segments. Several other genera and species are common in ponds.
The largest of the common water-beetles belong to the family Hydrophaide, which also includes numerous small and inconspicuous spe cies. In the form of the body and the fringed oar-like middle and hind legs they resemble the Dytiseide, from which all dte members of this family are distinguished by their short strongly clubbed The eggs are deposited in silken cocoons attached to water-plants or car ried by the female. In general resembling the water-tigers in form, the larva have shorter, thicker, solid jaws, much less prominent respira tory tubes and are less active, although, like them, carnivorous. They pupate in burrows in the banks of the ponds which they inhabit. The great water-beetle (Hydrobbiles triensgu leris) is a pitchy black polished beetle an inch and a half long, often seen flying at night or during the day rising to the surface of clear weed-grown ponds for air and, unlike the Dyhorde, usually resting head upward. In adult life they forsake the predaceous habits and animal diet of their larvae and become scavengers, finding their food chiefly in the vegetable debris at the bottom of ponds. Few inhabitants of fresh-water ponds and ditches are better suited to life in an .atinarium than these beetles and few present a greater variety or more interesting habits. Consult standard works, especially Miall, 'The Natural History of Aquatic Insects' (New York 1895) and Kellogg's 'American Insects' (New York 1909). See FIUME -WATER INSECTS.